In the field of ultra wideband transmission, there have been numerous methods devised to convert the radio frequency (RF) signal to baseband for further demodulation. One method uses a template pulse, a pulse similar to that of the received pulsed, generated within the receiver, correlated with, or simply multiplied with the received pulse and integrated to increase signal-to-noise ratio. Another example of this method is the transmit reference method which uses a delayed version of the received pulse as the template pulse. Another method correlates a sampling, or gating, pulse with the received. Impulse radios often use coherent detection methods, e.g., synchronous mixing of received pulses with gating pulses (also referred to as sampling pulses) or template pulses, along with integration of the output, to convert pulsed signals to base band. Gating pulses or template pulses are used as mixing pulses in order to increase pulse strength prior to integration. Typically, the mixing pulses are applied such that the template pulses substantially coincide with the peak of the received pulses.
A problem with these methods arises, however. The template and/or gating pulses are typically 150 picoseconds or less. For gigapulse transmission rates, the system must resample within 1 nanosecond. The template pulse generator, and correlator are iteratively powered and unpowered during this process resulting in two edges required for each conversion. These two edges must be carefully timed relative to one another and must have a rapid transition rate for high data rate systems. In addition, re-energizing the detection circuitry takes some appreciable amount of time and, thus creates inherent data latency. Current timing circuitry has difficulty responding to such a timing demand.
The time required to re-energize the detection circuitry at the sample rate places a limit on the achievable data rate. This is particularly relevant to high data rate systems, which tend to rely on high-chip rates to advance the data stream. High chipping rate systems are often preferred for very high data rate or high channel capacity systems. In these systems, events (pulses, clocks, samples, etc.) occur in rapid succession. Each event requires a settling time before a new event can occur without undue coupling from one to the next. Circuitry implementing these methods tends to be unduly complex and because of the amount of components involved, results in limits on the minimum size of devices employing this technology.
Thus, a new method for converting RF signals to baseband is required that requires less complex circuitry yet enables high chipping rates. In addition, an apparatus employing this method is needed.